Thermoplastic molding material exhibiting a high puncturing resistance and a good antistatic behavior

ABSTRACT

The molding composition comprises components A to C and, if desired, D: 
     a: as component A, from 20 to 94% by weight of a hard component made from one or more copolymers of styrene and/or α-methylstyrene with acrylonitrile, where the proportion of acrylonitrile is from 10 to 50% by weight, 
     b: from 5 to 70% by weight of at least one graft copolymer B, made from 
     b1: as component B1, from 10 to 90% by weight of at least one elastomeric particulate graft base with a glass transition temperature below 0° C., and 
     b2: as component B2, from 10 to 90% by weight of at least one graft made from a copolymer of styrene and/or α-methylstyrene with acrylonitrile, where the proportion of acrylonitrile is from 10 to 50% by weight, 
     c: as component C, from 0.1 to 10% by weight of at least one three-block copolymer of the formula X-Y-X with a central block Y made from propylene oxide units with an average molecular weight in the range from 2000 to 4000 and terminal blocks X made from ethylene oxide units whose average proportion in the three-block copolymer is from 2 to 35% by weight, 
     where the total weight of components A to C is 100% by weight, and 
     d: as component D, from 0 to 10% by weight, based on the total weight of components A to C, of other conventional auxiliaries and fillers.

The invention relates to thermoplastic molding compositions with highpuncture resistance and good antistatic performance. The moldingcompositions are impact-modified copolymers of styrene and/orα-methylstyrene with acrylonitrile.

Impact-modified styrene-acrylonitrile copolymers are used in a widevariety of applications. They are preferably used for producing moldingswhich are to have good mechanical properties. It is frequently necessaryfor molding compositions of this type to be given antistatic properties.This is generally done by adding an antistat to the moldingcompositions. To ensure sufficient breadth of application for themolding compositions it is desirable to make them suitable for a widerange of working conditions.

FR-B-1 239 902 has disclosed re sins which have been given antistaticproperties. Three-block copolymers of the formula X-Y-X can be added,inter alia, to molding compositions having polystyrene units,polyacrylo-nitrile units and polybutadiene units. Y here is apolypropylene oxide block with a molecular weight of from 1000 to 1800and each X is a polyethylene oxide block. The proportion of polyethyleneoxide is from 20 to 80%.

It is known from EP-B 0 018 591 that the abovementioned three-blockcopolymers of the formula X-Y-X can be added to styrene-acrylonitrilecopolymers with no rubber component. The addition increases the internallubrication of the molding compositions, giving an improvement inprocessing latitude in injection molding. The molecular weight of theblock Y in the three-block copolymer may be from 1200 to 3650, and theproportion of ethylene oxide units is from 10 to 30% by weight.

It is known from EP-A-0 135 801 that the abovementioned three-blockcopolymers of the formula X-Y-X can be added to polymer blends made frompolycarbonate and impact-modified styrene-acrylonitrile copolymer toimprove processing latitude. Here, the molecular weight of thepolypropylene oxide block Y is, for example, 1200, 2250 or 3600. Theproportion of ethylene oxide here is 10 or 40% by weight.

It is an object of the present invention to provide impact-modifiedcopolymers of styrene and/or α-methylstyrene with acrylonitrile whichhave increased puncture resistance and at the same time good antistaticperformance.

We have found that this object is achieved by means of a moldingcomposition made from components A to C and, if desired, D:

a: as component A, from 20 to 94% by weight of a hard component madefrom one or more copolymers of styrene and/or α-methylstyrene withacrylonitrile, where the proportion of acrylonitrile is from 10 to 50%by weight,

b: from 5 to 70% by weight of at least one graft copolymer B, made from

b1 : as component B1, from 10 to 90% by weight of at least oneelastomeric particulate graft base with a glass transition temperaturebelow 0° C., and

b2: as component B2, from 10 to 90% by weight of at least one graft madefrom a copolymer below 0° C., and

b2: as component B2, from 10 to 90% by weight of at least one graft madefrom a copolymer of styrene and/or α-methylstyrene with acrylonitrile,where the proportion of acrylonitrile is from 10 to 50% by weight,

c: as component C, from 0.1 to 10% by weight of at least one three-blockcopolymer of the formula X-Y-X with a central block Y made frompropylene oxide units with an average molecular weight in the range from2000 to 4000 and terminal blocks X made from ethylene oxide units whoseaverage proportion in the three-block copolymer is from 2 to 35% byweight,

where the total weight of components A to C is 100% by weight, and

d: as component D, from 0 to 10% by weight, based on the total weight ofcomponents A to C, of other conventional auxiliaries and fillers.

Molding compositions with components A, B and D and suitable to be giventhese properties have been described, for example, in DE-A-29 01 576 andin particular in the earlier document DE-A-197 28 629 which, however,was unpublished at the priority date of the present application.

The proportion of component A in the novel molding compositions ispreferably from 40 to 84.9% by weight, particularly preferably from 55to 79.7% by weight. The proportion of component B is preferably from 15to 50% by weight, particularly preferably from 20 to 40% by weight. Theproportion of component C is preferably from 0.1 to 5% by weight,particularly preferably from 0.3 to 2% by weight. The proportion ofcomponent D is preferably from 0 to 5% by weight, particularlypreferably from 0 to 3% by weight.

The proportion of acrylonitrile in component A is preferably from 10 to50% by weight, particularly preferably from 15 to 40% by weight, inparticular from 18.5 to 36% by weight.

In component B, the proportion of component B1 is preferably from 20 to80% by weight, particularly preferably from 25 to 75% by weight, and theproportion of component B2 is preferably from 20 to 80% by weight,particularly preferably from 25 to 75% by weight. The proportion ofacrylonitrile in component B2 here is preferably from 15 to 40% byweight, particularly preferably from 15 to 35% by weight.

In component C, the average molecular weight of the block Y made frompropylene oxide units is preferably from 2200 to 3800, particularlypreferably from 2300 to 3500, in particular about 2300, about 2750 orabout 3250, in each case +/−10%. The average proportion of the terminalblocks X made from ethylene oxide units, based on component C, ispreferably from 3 to 28% by weight, particularly preferably from 8 to24% by weight, in particular from about 8 to 14% by weight or from about18 to 24% by weight.

Component A

Component A preferably has a viscosity number VN (determined inaccordance with DIN 53726 at 25° C., 0.5% strength by weight indimethylformamide) of from 50 to 120 ml/g, particularly preferably from52 to 110 ml/g and in particular from 55 to 105 ml/g. It is particularlypreferably a styrene-acrylonitrile copolymer. Copolymers of this typeare obtained in a known manner by bulk, solution, suspension,precipitation or emulsion polymerization. Bulk and solutionpolymerization are preferred. Details of these processes are described,for example, in Kunststoffhandbuch, ed. R. Vieweg and G. Daumiller, vol.V “Polystyrol”, Carl-Hanser-Verlag Munich, 1969, pp. 118 ff.

Component B

Component B is a graft copolymer with an elastomeric particulate graftbase with a glass transition temperature below 0° C. The graft base heremay have been selected from all of the known suitable elastomericpolymers. It is preferably ABS (acrylonitrile-butadiene-styrene) rubber,ASA (acrylo-nitrile-styrene-alkyl acrylate) rubber, EPDM rubber,siloxane rubber or another rubber.

Component B1 is preferably at least one (co)polymer made from

b11: as component B11, from 60 to 100% by weight, preferably from 70 to100% by weight, of at least one conjugated diene, of a C₁-C₁₀-alkylacrylate, or of a mixture of these,

b12: as component B12, from 0 to 30% by weight, preferably from 0 to 25%by weight, of at least one monoethylenically unsaturated monomerdiffering from component B11, and

b13: as component B13, from 0 to 10% by weight, preferably from 0 to 6%by weight, of at least one crosslinking monomer.

Possible conjugated dienes B11 are in particular butadiene, isoprene,chloroprene and mixtures of these, and also the C₁-C₁₀-alkyl acrylateslisted below and mixtures of these. Preference is given to the use ofbutadiene or isoprene or mixtures of these, especially butadiene, or ofn-butyl acrylate.

The monomers present as component B12 may, if desired, be monomers whichvary the mechanical and thermal properties of the core within aparticular range. Examples of monoethylenically unsaturated comonomersof this type which may be mentioned are styrene, substituted styrenes,acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid,dicarboxylic acids, such as maleic acid and fumaric acid, and alsoanhydrides of these, such as maleic anhydride, nitrogen-functionalmonomers, such as dimethylamino-ethyl acrylate, diethylaminoethylacrylate, vinylimidazole, vinylpyrrolidone, vinylcaprolactam,vinylcarbazole, vinylaniline and acrylamide, C₁-C₁₀-alkyl esters ofacrylic acid, such as methyl acrylate, ethyl acrylate, n-propylacrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate,sec-butyl acrylate, tert-butyl acrylate and ethylhexyl acrylate, thecorresponding C₁-C₁₀-alkyl esters of methacrylic acid, and alsohydroxyethyl acrylate, aromatic and araliphatic esters of acrylic ormethacrylic acid, such as phenyl acrylate, phenyl methacrylate, benzylacrylate, benzyl methacrylate, 2-phenylethyl acrylate, 2-phenylethylmethacrylate, 2-phenoxyethyl acrylate and 2-phenoxyethyl methacrylate,N-substituted maleimides, such as N-methyl-, N-phenyl- andN-cyclohexylmaleimide, and unsaturated ethers, such as vinyl methylether, and also mixtures of these.

Preferred components B12 used are styrene, α-methylstyrene, n-butylacrylate, methyl methacrylate or mixtures of these, in particularstyrene and n-butyl acrylate or mixtures of these, especially styrene.If a component B12 is used but no component B13, the proportion ofcomponent B11 is preferably from 70 to 99.9% by weight, particularlypreferably from 90 to 99% by weight, and the proportion of component B12is preferably from 0.1 to 30% by weight, particularly preferably from 1to 10% by weight. Particular preference is given to butadiene-styrenecopolymers and n-butyl acrylate-styrene copolymers within the quantityrange given.

Examples of crosslinking monomers of component B13 are divinylcompounds, such as divinyl benzene, diallyl compounds, such as diallylmaleate, allyl esters of acrylic and methacrylic acid,dihydrodicyclopentadienyl acrylate (DCPA), divinyl esters ofdicarboxylic acids, for example of succinic acid or adipic acid, anddiallyl and divinyl ethers of dihydric alcohols, for example of ethyleneglycol or of 1,4-butanediol.

The graft B2 is preferably a styrene-acrylonitrile copolymer.

The graft copolymers B are usually prepared by the emulsionpolymerization process. This polymerization is generally carried out atfrom 20 to 100° C., preferably from 30 to 80° C. Conventionalemulsifiers are frequently added, for example alkali metal salts ofalkyl- or alkylarylsulfonic acids, alkyl sulfates, fatty alcoholsulfonates, salts of higher fatty acids having from 10 to 30 carbonatoms, sulfosuccinates, ether sulfonates or resin soaps. Preference isgiven to the use of the alkali metal salts, in particular the sodium orpotassium salts of alkylsulfonates or fatty acids having from 10 to 18carbon atoms.

The emulsifiers are generally used in amounts of from 0.5 to 5% byweight, in particular from 0.5 to 3% by weight, based on the monomersused in preparing the graft base.

The amount of water preferably used in preparing the dispersion is suchthat the finished dispersion has a solids content of from 20′ to 50% byweight. The water/monomers ratio usually used is from 2:1 to 0.7:1.

Free-radical generators suitable for initiating the polymerization areany of those which decompose at the selected reaction temperature, i.e.both those which decompose thermally on their own and those which dothis in the presence of a redox system. Preferred polymerizationinitiators are free-radical generators, for example peroxides, such aspreferably peroxosulfates (e.g. sodium persulfate or potassiumpersulfate) and azo compounds, such as azodiisobutyronitrile. However,it is also possible to use redox systems, in particular those based onhydroperoxides, such as cumin hydroperoxide.

The polymerization initiators are generally used in amounts of from 0.1to 1% by weight, based on the graft base monomers.

Both the free-radical generators and the emulsifiers are added to thereaction mixture, for example batchwise in the form of the entire amountat the beginning of the reaction, or batchwise and divided up into anumber of portions at the beginning and at one or more later junctures,or continuously over a particular period of time. The continuousaddition may also follow a gradient, which may, for example, rise orfall or be linear or exponential, or may also be stepped (stepfunction).

It is also possible to make concomitant use of molecular weightregulators, such as ethylhexyl thioglycolate, n-dodecyl or tert-dodecylmercaptan or other mercaptans, terpinols or dimeric methylstyrene, orother compounds suitable for regulating molecular weight. The molecularweight regulators are added to the reaction mixture batchwise orcontinuously, as described above for the free-radical generators andemulsifiers.

To maintain a constant pH, preferably of from 6 to 9, concomitant usemay be made of buffer substances, such as Na₂HPO₄/NaH₂PO₄, sodiumhydrogen carbonate, or buffers based on citric acid/citrate. Regulatorsand buffer substances are used in the customary amounts, and furtherdetails on this topic are therefore unnecessary.

In a particular embodiment, it is also possible to prepare the graftbase by polymerizing the monomers B1 in the presence of a finely dividedlatex (the seed latex method of polymerization). This latex is theinitial charge and may be made from monomers which form elastomericpolymers, or else from other monomers mentioned above. Suitable seedlatices are made from, for example, polybutadiene or polystyrene.

In another preferred embodiment, the graft base B1 may be prepared bythe feed method. In this process, the polymerization is initiated usinga certain proportion of the monomers, and the remainder of the monomersB1 (the “feed portion”) is added as feed during the polymerization. Thefeed parameters (shape of the gradient, amount, duration, etc.) dependon the other polymerization conditions. The principles of thedescriptions given in connection with the method of addition of thefree-radical initiator and/or emulsifier are once again relevant here.

Graft polymers with a number of “soft” and “hard” shells are alsosuitable.

The precise polymerization conditions, in particular the type, amountand method of addition of the emulsifier and of the other polymerizationauxiliaries, are preferably selected so that the resultant latex of thegraft polymer B has an average particle size, defined by the d₅₀ of theparticle size distribution, of from 80 to 800 nm, preferably from 80 to600 nm and particularly preferably from 85 to 400 nm.

In one embodiment of the invention, the reaction conditions are adjustedwith respect to each other in such a way that the polymer particles havebimodal particle size distribution, i.e. a size distribution with twomaxima developed to some extent.

The bimodal particle size distribution is preferably achieved by(partial) agglomeration of the polymer particles. This can be achieved,for example, by the following procedure: the monomers which form thecore are polymerized to a conversion of usually at least 90%, preferablymore than 95%, based on the monomers used. This conversion is generallyachieved after from 4 to 20 hours. The resultant rubber latex has anaverage particle size d₅₀ of not more than 200 nm and a narrow particlesize distribution (virtually monodisperse system).

In the second step, the rubber latex is agglomerated. This is generallydone by adding a dispersion of an acrylate polymer. Preference is givento the use of dispersions of copolymers of C₁-C₄-alkyl acrylates,preferably of ethyl acrylate, with from 0.1 to 10% by weight of monomerswhich form polar polymers, examples being acrylic acid, methacrylicacid, acrylamide or methacrylamide, N-methylolmethacrylamide andN-vinyl-pyrrolidone. Particular preference is given to a copolymer madefrom 96% of ethyl acrylate and 4% of methacrylamide. The agglomeratingdispersion may, if desired, also comprise more than one of the acrylatepolymers mentioned.

In general, the concentration of the acrylate polymers in the dispersionused for agglomeration should be from 3 to 40% by weight. For theagglomeration, from 0.2 to 20 parts by weight, preferably from 1 to 5parts by weight, of the agglomerating dispersion are used for each 100parts of the rubber latex, the calculation in each case being based onsolids. The agglomeration is carried out by adding the agglomeratingdispersion to the rubber. The addition rate is usually noncritical, andthe addition usually takes from about one to 30 minutes at from 20 to90° C., preferably from 30 to 75° C.

The rubber latex may also be agglomerated by other agglomerating agents,such as acetic anhydride, as well as by an acrylate polymer.Agglomeration by pressure or freezing is also possible. The methodsmentioned are known to the person skilled in the art.

Under the conditions mentioned, only some of the rubber particles areagglomerated, giving a bimodal distribution. More than 50%, preferablyfrom 75 to 95%, of the particles (distribution by number) are generallyin the non-agglomerated state after the agglomeration. The resultantpartially agglomerated rubber latex is relatively stable, and cantherefore easily be stored or transported without coagulation.

To achieve a bimodal particle size distribution of the graft polymer B,it is also possible to prepare, separately from one another in the usualmanner, two different graft polymers B′ and B″ differing in theiraverage particle size, and to mix the graft polymers B′ and B″ in thedesired mixing ratio.

The graft B2 may be prepared under the same conditions as those used forpreparing the graft base B1, and may be prepared in one or more steps.In two-stage grafting, for example, it is possible initially topolymerize styrene and/or α-methylstyrene alone, and then styrene andacrylonitrile, in two steps in succession. This two-stage grafting(firstly styrene, then styrene plus acrylonitrile) is a preferredembodiment. Further details concerning preparation of the graft polymersB are given in DE-A 12 60 135 and DE-A 31 49 358, and also in EP-A-0 735063.

It is advantageous in turn to carry out the graft polymerization ontothe graft base B1 in an aqueous emulsion. It may be undertaken in thesame system as that used for polymerizing the graft base, and furtheremulsifier and initiator may be added. These do not have to be identicalwith the emulsifiers and/or initiators used for preparing the graft baseB1. For example, it may be expedient to use a persulfate as initiatorfor preparing the graft base B1 but a redox initiator system forpolymerizing the graft shell B2. Otherwise, that which was said for thepreparation of the graft base B1 is applicable to the selection ofemulsifier, initiator and polymerization auxiliaries. The monomermixture to be grafted on may be added to the reaction mixture all atonce, in portions in more than one step or, preferably, continuouslyduring the polymerization.

If non-grafted polymers are produced from the monomers B2 during thegrafting of the graft base B1, the amounts, which are generally lessthan 10% by weight of B2, are attributed to the weight of component B.

Component C

The three-block copolymer of the formula X-Y-X used according to theinvention may be prepared in a manner known per se (N. Schbnfeldt,Grenzflachenaktive Ethylenoxid-Addukte, WissenschaftlicheVerlags-gesellschaft mbH, Stuttgart, 1976, pp. 53 ff.) bypolymerization, firstly preparing central polypropylene oxide block Y,to both ends of which is added a block made from ethylene oxide units.The molecular weights given above are generally average molecularweights (number average M_(n), for example determined from the OH numberin accordance with DIN 53240).

Preferred three-block copolymers and their preparation are alsodescribed in EP-A-0 135 801 and EP-A-0 018 591.

Component D

Other customary auxiliaries and fillers may be used as component D.Examples of substances of this type are lubricants and mold-releaseagents, waxes, pigments, dyes, flame retardants, antioxidants,stabilizers to protect against the effect of light, fibrous orpulverulent fillers, fibrous or pulverulent reinforcing agents, andantistats, and also other additives, or mixtures of these.

Examples of suitable lubricants and mold-release agents are stearicacids, stearyl alcohol, stearates and stearamides, and also siliconeoils, montan waxes and waxes based on polyethylene and polypropylene.

Examples of pigments are titanium dioxide, phthalocyanines, ultramarineblue, iron oxides and carbon black, and also the entire class of organicpigments.

For the purposes of the invention, dyes are any of the dyes which can beused for transparent, semitransparent or nontransparent coloration ofpolymers, in particular those which are suitable for coloring styrenecopolymers. Dyes of this type are known to the person skilled in theart.

Examples of flame retardants which may be used are thehalogen-containing or phosphorus-containing compounds known to theperson skilled in the art, magnesium hydroxide, and other commoncompounds or mixtures of these. Red phosphorus is also suitable.

Particularly suitable antioxidants are sterically hindered mononuclearor polynuclear phenolic antioxidants, which may have varioussubstituents or be bridged via substituents. These include, besidesmonomeric compounds, oligomeric compounds which can be built up from anumber of fundamental phenol units. Other possible compounds arehydroquinones and hydroquinone analogs and substituted compounds, andalso antioxidants based on tocopherols and on derivatives of these. Itis also possible to use mixtures of different antioxidants. In principleit is possible to use any of the compounds which are commerciallyavailable or suitable for styrene copolymers, for example Topanol® orIrganox®.

Together with the phenolic antioxidants given as examples above,concomitant use may be made of costabilizers, in particular thosecontaining phosphorus or containing sulfur. P- or S-containingcostabilizers of this type are known to the person skilled in the artand are available commercially.

Examples of suitable stabilizers to protect against the effect of lightare various substituted resorcinols, salicylates, benzotriazoles,benzophenones and HALS (hindered amine light stabilizers), availablecommercially for example as Tinuvin®.

Examples which may be mentioned as fibrous or pulverulent fillers arecarbon fibers or glass fibers in the form of glass fabrics, glass matsor glass filament rovings, chopped glass, glass beads, and alsowollastonite, particularly preferably glass fibers. If glass fibers areused, these may have been provided with a size and a coupling agent toimprove compatibility with the components of the blend. The glass fibersmay be incorporated either as short glass fibers or ascontinuous-filament strands (rovings).

Suitable particulate fillers are carbon black, amorphous silica,magnesium carbonate, chalk, powdered quartz, micas, bentonites, talc,feldspar, or, in particular, calcium silicates, such as wollastonite, orkaolin.

Each of the individual additives is used in the usual amounts, andtherefore no further details on this topic are required.

Preparation of the Molding Compositions

The molding compositions are preferably prepared by separate preparationof the individual components A to C and, if desired, D, and then mixingthe components.

Processes suitable for preparing the molding compositions are described,for example, in EP-A-0 135 801, EP-B-0 018 591 and, in particular,DE-A-197 28 628.

The novel molding compositions may be used for producing moldings,fibers or films. Processes of this type for producing moldings, fibersand films are listed in the publications mentioned.

The invention is described in greater detail below, using examples.

EXAMPLES 1. Preparation of the Graft Polymer B

1.1 Preparation of the Graft Base B1

43,120 g of the monomer mixture given in Table 1 are polymerized at 65°C. in the presence of 432 g of tert-dodecyl mercaptan (TDM), 311 g ofthe potassium salt of C₁₂-C₂₀ fatty acids, 82 g of potassium persulfate,147 g of sodium hydrogencarbonate and 58,400 g of water, to give apolybutadiene latex. The details of the process are described in EP-A-0062 901, Ex. 1, p. 9, line 20 to p. 10, line 6. The conversion was 95%or greater. The average particle size d₅₀ of the latex was from 80 to120 nm.

To agglomerate the latex, 35,000 g of the resultant latex wereagglomerated at 65° C. by adding 2700 g of a dispersion (solids content10% by weight) made from 96% by weight of ethyl acrylate and 4% byweight of methacrylamide (partial agglomeration).

For use of an n-butyl acrylate polymer as graft base B1 the procedureused is as in EP-A-0 735 063, Comparative Examples 1, 2, 14 and 15.

1.2 Preparation of the Graft B2

9000 g of water, 130 g of the potassium salt of C₁₂-C₂₀ fatty acids and17 g of potassium peroxodisulfate were added to the agglomerated latex.The monomer mixtures given in Table 2 were then added, with stirring, at75° C. within a period of 4 hours. Conversion, based on the graftmonomers was virtually quantitative.

The resultant graft polymer dispersion with bimodal particle sizedistribution had an average particle size d₅₀ of from 150 to 350 nm anda d₉₀ of from 400 to 600 nm. The particle size distribution had a firstmaximum in the range from 50 to 150 nm and a second maximum in the rangefrom 200 to 600 nm.

The resultant dispersion was mixed with an aqueous dispersion of anantioxidant then coagulated by adding a magnesium sulfate solution. Thecoagulated rubber was centrifuged off from the dispersion water, andwashed with water. This gives a rubber with about 30% by weight ofresidual water adhering to or enclosed within the product.

TABLE 1 Graft base B1 Example R1 R2 Monomers [% by weight] Butadiene 1000 Crosslinking agent 0 2 n-Butyl acrylate 0 98 Properties: Swellingindex 32 Gel content [%] 70

R2 was obtained in accordance with DE-A-31 49 358.

TABLE 2 Graft B2 and finished graft polymer B Component Ba Bb Bc Graftbase from Example R1 R2 R1 Monomers [% by weight] Styrene 80 75 70Acrylonitrile 20 25 30

2. Preparation of the Polymers A

The thermoplastic polymers A were prepared by the continuous solutionpolymerization process as described in Kunststoff Handbuch, ed. R.Vieweg and G. Daumiller, Vol. V “Polystyrol”, Carl-Hanser-Verlag,Munich, 1969, pp. 122-124. Table 3 gives the formulations andproperties.

TABLE 3 Components Components Aa Ab Ac Monomers [% by weight] Styrene 7675 67 Acrylonitrile 24 25 33 Viscosity number 67 80 60 VN [ml/g]

3. Preparation of the Blends Made From Components A and B

Blending After Graft Rubber B had Been Dried

The graft rubber B comprising residual water was dried in vacuo usingwarm air and intimately mixed with the other component A in a Werner &Pfleiderer ZSK 30 extruder at 250° C. and 250 min⁻¹, with a throughputof 10 kg/h. The molding composition was extruded and the molten polymermixture was subjected to rapid cooling by passing into a water bath at30° C. The solidified molding composition was pelletized.

4. Tests Carried Out

Swelling index of graft base B1: a film was produced by evaporating thewater from the aqueous dispersion of the graft base. 0.2 g of this filmwere mixed with 50 g of toluene. After 24 hours the toluene was removedfrom the swollen specimen under reduced pressure and the specimen wasweighed. The specimen was weighed again after 16 hours' drying in vacuoat 110° C. The values calculated were:${{Swelling}\quad {index}\quad {SI}} = \frac{\begin{matrix}{{Weight}\quad {of}\quad {the}\quad {swollen}\quad {specimen}\quad {after}\quad {removal}} \\{{of}\quad {solvent}\quad {at}\quad {reduced}\quad {pressure}}\end{matrix}}{{Weight}\quad {of}\quad {the}\quad {specimen}\quad {dried}\quad {in}\quad {vacuo}}$${{Gel}\quad {content}} = {{\frac{{Weight}\quad {of}\quad {the}\quad {specimen}\quad {dried}\quad {in}\quad {vacuo}}{{Initial}\quad {weight}\quad {of}\quad {specimen}\quad {before}\quad {swelling}} \cdot 100}\%}$

Particle Sizes in the Rubber Latex:

The average particle size d given is the weight-average particle size asdetermined using an analytical ultracentrifuge and the method of W.Scholtan and H. Lange, Kolloid-Z. and Z.-Polymere 250 (1972), pp.782-796. The ultracentrifuge measurement gives the integral weightdistribution of particle diameter in a specimen. From this it can beseen what percentage by weight of the particles have a diameter smallerthan or equal to a particular size. The d₁₀ is a particle diameterselected in such a way that the diameters of 10% by weight of all of theparticles are smaller, and those of 90% by weight are larger. Thereverse applies to the d₉₀ : 90% by weight of all of the particles havesmaller diameters, and 10% by weight larger diameters, than the d₉₀ .The weight-average particle diameter d₅₀ and the volume-average particlediameter d₅₀ are particle diameters selected in such a way that theparticle diameters of, respectively, 50% by weight and 50% by volume ofall of the particles are larger and those of, respectively, 50% byweight and 50% by volume are smaller. d₁₀, d₅₀ and d₉₀ describe thebreadth Q of the particle size distribution, where Q=(d₉₀−d₁₀)/d₅₀. Thesmaller is Q, the narrower is the distribution.

Viscosity number VN: this was determined in accordance with DIN 53726 ona 0.5% strength by weight solution of the polymer in dimethylformamide.

To determine the mechanical and antistatic values below, test specimenswere injection molded from pellets of the molding compositions. Thespecimens were standard small specimens (see DIN 53453), dumb-bellspecimens, disks of diameter 60 mm and thickness 2 mm and rectangularsheets of thickness 2 mm. In each case the melt temperature was 250° C.and the mold temperature 60° C., unless otherwise stated.

Vicat: the Vicat heat distortion temperature was determined on pressedsheets in accordance with ISO 306/B with a load of 50 N and a heatingrate of 50 K/h.

w_(p): the penetration energy w_(p) was determined in accordance withISO 6603-2 on disks or rectangular sheets of 40×40 mm, using thePlastechon test at 23° C. The test specimens had been produced at a melttemperature of 250° C.

Antistatic Performance:

1.) Dust chamber test: the dust in a dust chamber is whirled for 10 sec.Any large amounts of dirt adhering are removed by blowing, and a visualassessment is made of the dust coating.

2.) On disks (diameter 60 mm, thickness 2 mm) using the corona method(based on DIN VDE 0303 T.3). E (15), the residual charge present after15 min is taken as a measure of the effectiveness of the antistat.

Example 1c (Comparative)

A mixture of 66% by weight of component Aa and 34% by weight ofcomponent Ba was extruded (Werner & Pfleiderer ZSK 30) at 250° C., theheat distortion temperature was determined and antistatic performancewas tested in the dust chamber. The results are listed in Table 4.

Examples 2c to 8c, 9 and 10

A mixture of 66% by weight of component Aa and 34% by weight ofcomponent Ba was extruded (Werner & Pfleiderer ZSK 30) at 250° C. withthe antistats given in Table 4, the heat distortion temperature wasdetermined and antistatic performance was tested in the dust chamber.The results are listed in Table 4.

Example 11c (Comparative)

A mixture of 71% by weight of component Ab and 29% by weight ofcomponent Ba was extruded (Werner & Pfleiderer ZSK 30) at 250° C., theheat distortion temperature was determined and the corona test was usedto test antistatic performance. Puncture performance was also tested.The results are listed in Table 5.

Examples 12c and 13 to 15

A mixture of 71% by weight of component Ab and 29% by weight ofcomponent Ba was extruded (Werner & Pfleiderer ZSK 30) at 250° C. withthe antistats given in Table 5, the heat distortion temperature wasdetermined and the corona test was used to test antistatic performance.Puncture performance was also tested. The results are listed in Table 5.

As can be seen from the examples, neither ethylene oxide homopolymersnor propylene oxide homopolymers are effective. Only EO/PO three-blockcopolymers with a PO block of from 2000 to 4000 and an EO fraction below30% by weight are effective as antistat and mechanical propertyenhancer.

Examples 16c, 17 and 18

A mixture of 71% by weight of Ac and 29% by weight of Bc was extruded at250° C. with the antistats given in Table 6, and the dust chamber testwas used to determine antistatic performance. Puncture performance wasalso tested.

TABLE 4 Molding Heat composition % by weight EO fraction PO fractionTotal molecular distortion from of (% by (% by MW of weight (numbertemperature Dust coat Example auxiliary weight) weight) PO blockaverage) (° C.) formation  1c 96 pronounced  2c 1 100 600 92.1pronounced  3c 1 100 1500 93.9 pronounced  4c 1 100 600 93.4 pronounced 5c 1 100 2000 94.5 moderate to pronounced  6c 1 100 4000 94.5pronounced  7c 1 10 90 1750 92.8 pronounced  8c 1 30 70 3250 93.4pronounced  9 1 10 90 2300 95.4 moderate 10 1 10 90 3250 95.4 weak tomoderate

TABLE 5 Molding Heat composition % by weight EO fraction PO fractiondistortion from of (% by (% by MW of Penetration temperature Exampleauxiliary weight) weight) PO block (Nm) (° C.) E (15) (%) 11c 16 97.1 2312c 1 80 20 1750 29.5 94.9 22 13 1 10 90 2300 29.6 96.4 56 14 1 20 802750 26.3 94.9 50 15 1 10 90 3250 28.5 96.6 44

TABLE 6 Molding composition % by weight EO fraction PO fraction from of(% by (% by MW of Penetration Dust coat Example auxiliary weight)weight) PO block (Nm) formation 16c — 19.3 Pronounced 17 0.7 10 90 230044.1 moderate 18 0.9 10 90 2300 42.0 moderate- weak

We claim:
 1. A molding composition A consisting of components A to Cand, optionally, D: a: as component A, from 20 to 94% by weight of ahard component consisting of one or more copolymers of styrene and/orα-methylstyrene with acrylonitrile, where the proportion ofacrylonitrile is from 10 to 50 by weight, b: from 5 to 70% by weight ofat least one graft copolymer B, consisting of b1 : as component B1, from10 to 90% by weight of at least one elastomeric particulate graft basewith a glass transition temperature below 0° C., and b2: as componentB2, from 10 to 90% by weight of at least one graft moiety grafted to thegraft base B1, said graft moiety consisting of a copolymer of styreneand/or α-methylstyrene with acrylonitrile, where the proportion ofacrylonitrile is from 10 to 50% by weight, c: as component C, from 0.1to 10% by weight of at least one three-block copolymer of the formulaX-Y-X with a central block Y consisting of propylene oxide units with anumber average molecular weight in the range from 2000 to 4000 andterminal blocks X consisting of ethylene oxide units whose averageproportion in the three-block copolymer is from 2 to 28% by weight,where the total weight of components A to C is 100% by weight, and d: ascomponent D, from 0 to 10% by weight, based on the total weight ofcomponents A to C, of other conventional auxiliaries and fillersdifferent from components A to C, selected from the group consisting oflubricants and mold-release agents, waxes, pigments, dyes, flameretardants, antioxidants, stabilizers to protect against the effect oflight, fibrous or pulverulent fillers, fibrous or pulverulentreinforcing agents, antistats, and mixtures thereof.
 2. A moldingcomposition as claimed in claim 1, wherein component A is astyrene-acrylonitrile copolymer.
 3. A molding composition as claimed inclaim 1, wherein component B1 is at least one (co)polymer consisting ofb11: as component B11, from 60 to 100% by weight of at least oneconjugated diene, of a C₁-C₁₀-alkyl acrylate, or of a mixture of these,b12: as component B12, from 0 to 30% by weight of at least onemonoethylenically unsaturated monomer differing from component B11, andb13: as component B13, from 0 to 10% by weight of at least onecrosslinking monomer.
 4. A molding composition as claimed in claim 1,wherein, in component C, the number average molecular weight of theblock Y is from 2200 to 3400 and the average proportion of blocks X inthe three-block copolymer is from 5 to 25% by weight.
 5. A process forpreparing a molding composition as claimed in claim 1, by separatepreparation of the individual components A to C and, optionally, D, andthen mixing the components.
 6. A molding, a fiber or a film consistingof a molding composition as claimed in claim 1.